nation, fighting the flu. And tonight, some new post cards from the front lines of america's epidemic. Now, even worrying countries overseas. You can see it here. Look. Passengers from chicago are arriving in south korea, being scanned by those thermal cameras for signs of fever. And, we are also hearing of churches back home asking sick parishioners to refrain from shaking hands or drinking wine from the large chalice at communion. And more and more, the all-american high five is being replaced by the fist bump to contain the spread of the flu. And today, we learned that almost 70 million americans believe the flu shot will give them the flu. So, we asked abc's chief medical editor dr. Richard besser to bring us back the truth. I actually have not gotten a flu shot. No, I haven't had the flu shot this year. I don't think I need it. I haven't had time. Every time I get the flu shot I get sick afterwards. Someone needs to do a better job of convincing me to get the flu shot. I just think I'll get the flu if I get the flu shot. Reporter:69 million other americans agree with her, thinking the flu shot will give them the flu. And right outside our abc offices -- how can you get the flu from the flu shot? That's what they say. Reporter: How can the flu shot give you the flu? Because it's a vaccine. And to make the vaccine, you have to put some of the, like, bacteria in it -- you have to put the virus in it. Reporter: I see the confusion. But let me set all 69 million of you straight. Getting the flu vaccine does not give you the flu. Think of the shot as a video game. The shot is made of parts of three dead flu viruses. Dead. Not whole viruses. They don't work, they can't give you the flu. Your immune system studies those virus parts, sees how they're made and in about two weeks, builds weapons, antibodies, that will fight the live version of that virus. And if you breathe in those strains of live flu, you'll have some immune system weapons that shoot that virus down. Did you get your flu shot this year? No. Not this year. Reporter: You might want to think again. Out on the street tonight, drichlt richard besser is here. So, rich, you swear, you say it cannot give you the flu. But afterwards, if you feel that soreness, a little ache, sometimes a tiny bit of fever, it is -- Reporter: You can feel those. And it's your body reacting. It's building those anti-bodies. So, what I tell my patients, if you feel that sore arm and that fever, it's going to work even better for you. That can give you some comfort. The more you're feeling, the more you're building up ant anti-bodies. Reporter: Your body is building up. It's not too late to get the flu shot? Reporter: As long as you are seeing the flu, it's still out there, there's time to be protected. Maybe six weeks, maybe longer. And we are hearing the protection is about 62%. But think about it as a seat belt. It doesn't protect you against everything, but it protects you against a lot. It's a really smart way to go. And you say it begins to work just a couple of days after you get it, full effect, two weeks, but it begins to work right away. Reporter: That's right. Okay, dr. Richard besser, thank you so much.

This transcript has been automatically generated and may not be 100% accurate.